The present invention relates to a process for producing rigid foams with improved insulation characteristics (as measured by K-factor) and to the foams produced by this process.
Rigid polyurethane foams and processes for their production are known. Such foams are typically produced by reacting an isocyanate with an isocyanate-reactive compound such as a polyol in the presence of a blowing agent. Chlorofluorocarbons were the blowing agents most commonly used until recently. However, when it became known that these chlorofluorocarbons posed environmental problems, the search for alternative blowing agents began.
Among the blowing agents considered to be promising alternatives to the chlorofluorocarbons (CFCs)are the hydrogen-containing chlorofluorocarbons (HCFCs), highly fluorinated compounds (HFCs) and mixtures of HCFCs and HFCs. HCFC-141b is one of the more promising alternative blowing agents and has been the subject of a number of publications.
U.S. Pat. No. 5,397,808, for example, discloses low thermal conductivity foams made with a combination of HCFC-141b, perfluorinated compounds and carbon black. The perfluorinated compounds taught to be useful in this blowing agent combination include perfluorinated aliphatic hydrocarbons, perfluorinated cycloaliphatic hydrocarbons, perfluorinated N-aliphatic amino ethers, cyclic amino ethers, 1,3- or 1,4-amino ethers, perfluorinated ethers and perfluorinated tertiary alkylamines.
U.S. Pat. No. 5,318,996 discloses rigid insulating polyurethane foams prepared from ternary blowing agent mixtures which blowing agent mixtures were composed of water, HCFC-22 or HCFC-141b and a perfluorinated hydrocarbon having from 3 to 8 carbon atoms.
U.S. Pat. No. 4,927,863 discloses a process for the production of closed-cell polyurethane foams in which a mixture of a 2 carbon hydrogen-containing halocarbon (such as HCFC-141b and HCFC-123) with a shrinkage-minimizing halocarbon such as any of the known CFCs, HCFC-22, HFC-32, HCFC-124, HCFC-133a, HFC-134a, HCFC-142b and HFC-152a is used as the blowing agent.
U.S. Pat. No. 4,960,804 discloses rigid foams produced using a blend of a chlorofluorocarbon and an alkyl alkanoate as the blowing agent. HCFC's such as 1,1-dichloro-2,2,2-trifluoroethane and 1,1-dichloro-1-fluoroethane are among the chlorofluorocarbons taught to be suitable.
U.S. Pat. No. 4,996,242 discloses polyurethane foams made with two different halocarbons and an inert organic liquid are combined in specified amounts to form a ternary mixture which mixture is used as the blowing agent. The halocarbons taught to be suitable blowing agents for the disclosed ternary mixtures include at least one halocarbon having a boiling point below about 10.degree. C. and at least one halocarbon having a boiling point from about 20.degree. to about 35.degree. C. Halocarbons having boiling points below 10.degree. C. include 1,1-difluoroethane, 1,1,1-chlorodifluoroethane, 1-chloro-1,1,2,2,-tetrafluoroethane, 1-chloro-1,1,1,2-tetrafluoroethane and mixtures thereof. Halocarbons having a boiling point from 20.degree. to 35.degree. C. include trichlorofluoromethane, 1,1-dichloro-2,2,2-trifluoroethane, 1,1,1-dichlorofluoroethane. The inert organic liquids which are included in these ternary mixtures include pentane and substituted pentanes, hexane and substituted hexanes and haloalkanes.
U.S. Pat. No. 5,057,547 discloses mixtures of specific chlorofluorocarbons and specific hydrocarbons which are useful in the production of rigid, closed cell foams. The chlorofluorocarbons useful in these disclosed mixtures include 2,2-dichloro-1,1,1-trifluoroethane and 1,1-dichloro-1-fluoroethane. The hydrocarbons useful in these mixtures include n-pentane, 2-methyl butane, hexane, the position isomers of hexane and mixtures thereof.
U.S. Pat. No. 5,162,384 discloses foamed plastics made with blowing agent emulsions composed of at least one low boiling perfluorinated, N-aliphatic, cyclic 1,3- or 1,4-aminoether blowing agent, a foamable reaction mixture and a fluorochemical surfactant.
U.S. Pat. No. 5,164,418 discloses a process for producing foams using fluoroalkanes represented by the formula C.sub.a H.sub.b F.sub.c are used as the blowing agent.
U.S. Pat. No. 5,254,601 and 5,272,183 each discloses HCFC-Blown rigid foams having low thermal conductivities. These foams are produced using a blowing agent mixture that includes from about 0.1 to about 1.0% by weight water and 1,1-dichloro-2,2,2-trifluoroethane or dichlorofluoroethane.
U.S. Pat. No. 5,314,926 discloses foams blown with mixtures of 1,1,12,3,3,3-heptafluoropropane and one or more hydrocarbons or partially halogenated alkanes.
U.S. Pat. No. 5,470,891 discloses rigid polyisocyanate-based foams which are produced using water and a C.sub.1-4 hydrofluorocarbon having a boiling point of 300.degree. K or less as the blowing agent.
U.S. Pat. No. 5,496,866 discloses polyfluoroalkanes which are useful as propellants. Water and other highly volatile organic substances may optionally be included in a foam-forming mixture in addition to these polyfluoroalkanes.